In an Ottawa high school, a committee of staff and student representatives explored drug use in the school. A questionnaire was developed to assess student perception of academic performance and extracurricular involvement; students' frequency of drug use during the previous two months for nine categories of drugs; time and place of use and source of drugs; and student opinions of the degree of harmfulness of various drugs and their reasons for using drugs. Questionnaires were completed by 1230 high school students during the 1980-81 school year. Results revealed that alcohol was the most frequently used substance, followed by marijuana, LSD, and cocaine. Use of angel dust, heroin, and solvents was rarely reported. Use of alcohol, marijuana, and LSD increased sharply between grades 9 and 11 but little after that. Friends or relatives were reported to be the most frequent source of drugs, while nearly half of the users had obtained drugs from a dealer at least some of the time. Students rated alcohol and marijuana at least harmful; cigarettes, drugs from a drugstore, cocaine, solvents, LSD, heroin, and angel dust were ranked in a "more" to "most" harmful order. Sex differences in drug use were not statistically significant. Comparisons with earlier studies suggest that high school students in 1970, 1977, and 1981 are in general agreement about the harmfulness of certain drugs. (NRB)